It is well known that in many internal combustion engines the fuel is also the lubricant for the fuel system components, such as fuel pumps and injectors. Many studies of fuels with poor lubricity have been conducted in an effort to understand fuel compositions that have poor lubricity and to correlate lab test methods with actual field use. The problem is general to diesel fuels, kerosene and gasolines, however, most of the studies have concentrated on the first two hydrocarbon fuels.
Since the advent of low sulfur diesel fuels in the early 1990s, relatively large amounts of lubricity additives have been used to provide a fuel that does not cause excessive wear of engine parts. Unfortunately, many commercially available fuel additives tend to freeze or form crystals at lower temperatures common during winter weather. The freezing or formation of crystals makes handling of the additives, and particularly their injection into fuel, difficult. Blending the fuel additive with a solvent can lower the freezing point and reduce the crystal formation temperature, or cloud point. However, addition of a solvent may increase cost and preparation complexity.
Some of the fuel additives presently used may have the disadvantage of solidifying on storage at low temperatures. Often even at room temperature, crystalline fractions may separate and cause handling problems. Diluting the additives with organic solvents only partly solves the problem, since fractions may still crystallize out from solutions or the solution may gel and solidify. Thus, the additives either have to be greatly diluted or kept in heated storage vessels and added via heated pipework.
Thus, it would be desirable if a way could be discovered to enhance the lubricity of a distillate fuel, but the fuel remains homogeneous, clear and flowable at low temperatures. Further, the cold flow properties of a middle distillate fuel with the additive should not be significantly adversely affected.